Avoid potential divide by zero in LightSource.hillshade

joferkington · joferkington · commit 108eac73ecd2 · 2014-07-23T07:24:54.000-05:00
diff --git a/lib/matplotlib/colors.py b/lib/matplotlib/colors.py
@@ -1561,8 +1561,13 @@ def hillshade(self, elevation, vert_exag=1, dx=1, dy=1, fraction=1.):
             np.clip(intensity, imin, imax, intensity)
 
         # Rescale to 0-1, keeping range before contrast stretch
-        intensity -= imin
-        intensity /= (imax - imin)
+        if imax > imin:
+            intensity -= imin
+            intensity /= (imax - imin)
+        else:
+            # If constant slope, keep relative scaling 
+            # (i.e. flat should be 0.5, fully occluded 0, etc.)
+            intensity = (intensity + 1) / 2
 
         return intensity
 
